Pump with pressure bushing



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PUMP WITH PRESSURE BUSHING Filed Aug. 16. 1943 4 Sheets-Sheet 4 C; 11'reven e),-

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Patented June 29, 1948 PUMP WITH PRESSURE BUSHING John A. Lauck, SouthEuclid, Ohio, alaignor, by

mesne assignments, to Borg-Warner Corporation, Chicago, 111., acorporation of Illinois Application August 1c, 194:, ser al No. 49s,?

3 Claims. (01. 103-126) This invention is directed to high pressure geartype liquid displacing devices, and particularly to an improvedarrangement for maintaining axial adjustable end of plate or bearingbushings in sealed contact with the side faces of the associated gears.

It is an object of this invention to provide an improved arrangement ofpressure operating means efl'ecting and maintaining the requisite sealedengagement between the end bushings and the associated faces of thegears, notwithstanding the fact that high output pressures are reachedwhich result in enormous pressures between the gears and the bushingstending to effect separation thereof with a resulting loss of volumetricemciency. This invention is closely related in object to copending Rothand Lauck Serial No. 439,030, filed April 15, 1942, and issued as Patent2,420,622 of May 13, 1947, and is considered as presenting still anotherimproved solution to the same general problem.

Since it is desired to cause a sealing action between the gears and theassociated face plate or. as herein described, movable bushing bearing,in the direction of the associated gear faces, which has a smalldifferential value or increment greater than the oppositely actinpressure between the gear faces and the bushing, is an object todisclose a construction which will accomplish this desired feature.

It is a further object or feature of this invention to provide a bushingmeans wherein the bushing is movable to and away from the face of theassociated gears, and in which the liquid pressure from the outlet ofthe gears operates to load the bushing urging it against the gearswhereby a sealing action with the face of the gears is accomplished. Inthis connection, it is an object to provide a construction in which theload urging the bushing against the gears will always predominate forthe pumping action by a small amount over the oppositely acting forcetending to separate the bushings from the gears.

In this connection, it is a further obiect to present a construction inwhich the fluid used in loading the gears is manually controlled by arelease means which prevents overloading the bushing, and further, it isan object to provide an arrangement incorporating one or more meteringvalves in the fluid conduit system between the pump outlet and thebushing loading surfaces.

It is a further object of this invention to provide an outlet liquidpressure operated unbalanced bushing and bearing construction of theabove type in combination with an arrangement providing for automaticreversal of the direction of operation in response only to the reverserotation of the gear, without requiring any special adjustment orreversal of other parts.

It is a still further object to provide, in a high pressure liquiddisplacement gear device of the present type, any improved arrangementfor establishing and maintaining a plurality of liquid pressure zoneseach having an important function in connection with the operation ofthe end plate or bushing and associated coupling seal.

It is a further object of the invention to provide a bona fide form ofconstruction in which the movable end plate or bushing bearing is loadedin whole or in part by separate piston means. In this arrangement, it isa feature to present a construction in which the load may be distributedto the portion of the bearing on which the greatest pressure tending tomove the bearing away from the gears is exercised. It is a furtherfeature to present a construction in which the proper portion of thebearing is loaded by piston means or otherwise regardless of thedirection the pump rotates, it being understood that a reversal ofdirection of the pump changes the portion of the bearing which is mostheavily loaded.

It is an object to present an improved arrangement which is relativelysimple to manufacture, which lends itself to modern manufacturingoperation, and which is rugged and durable in operation.

Other and more particular objects, advantages and uses of my inventionwill become apparent from a reading of the following specification,taken in connection with the accompanying drawings forming a partthereof and wherein:

Fig. 1 is an axial broken-away sectional view, showing the essentialelements of a gear pump incorporating a preferred embodiment of myinvention;

Fig. 2 is a cross-sectional view taken substantially on the line 2-2 ofFig. 1;

Fig. 3 is a view corresponding generally to that of Fig. l, but showinga modified form wherein separate piston means are used to load themovable bearing, and wherein a metering and relief means are disclosedfor controlling th fluid pressure exerted on the movable flange bearing;

Fig. 4 indicates diagrammatically the distribution of pressure in apumping operation wherein the gears of a gear pump operate withdifferent pressures at different positions with the consequent result,the view being a fragmentary crosssectional view to the Rear wheel of apump corresponding to those disclosed herein.

Fig. 5 is an axial sectional view of another modified construction, thisview being slightly fragmentary, and serving to show a somewhatdifferent arrangement of sealing valve and piston loading means.

Fig. 6 is a cross-sectional view taken on the line 6-6 of Fig. 5 and 8-6of Fig. 7 looking in the direction of the arrows;

Fig. 7 is a cross-sectional view taken on the line 1-4 of Fig. 5 lookingin the direction of the arrows;

Fig. 8 illustrates still another modification, the view illustrating thepiston loading of the movable bearing with the use of a. metering valve;

Fig. 9 is a view taken on the line 5-9 of Fig. 8, looking in thedirection of the arrows; and

Fig. 10 is a view taken on the line ill-i of Fig. 8 illustratingparticularly the valve arrangement controlling the flow of fluid in thebushing loading piston.

Referring more in detail to the drawings. and referring first to theconstruction shown in Figs. 1 and 2 in particular, in indicatesgenerally a gear type pump with certain conventional portions thereofbroken away for the purpose of clarity, the pump including especially ahousing I l formed with a pair of internal overlapping bores l2 and I3,receiving therein a pair of gears M and i5, meshing in the general areaof overlap of said bores.

Leading to and from said gears l4 and ii, in the area of meshingtherebetween, are a pair of main flow passages l and I1, either of whichmay become the inlet or the discharge passage depending upon thedirection of rotation of the gears l4 and ii. The actual terminalconnections forming part of the housing have been shown broken away forthe purpose of simplicity. it not being deemed necessar to show thisconventional structure.

Gears I4 and i5, as will be apparent from Figs. 1 and 2 each includeoppositely extending trunnions, journals, or shafts, seated in bearingmembers as hereinafter more fully described and, as is apparent from thedrawing, the bearing members are received in reduced extensions on bothsides of the bores l2 and i3. Only the journals ISA and IE3 0f the gearI5 are shown in detail since the corresponding journals of gear I! areidentical therewith except that Journal IE3 is provided with a splinedextension |5C cooperating with a flexible coupling I8, including a shaftID for driving gear i5 and a flexible sealing ring iBA.

For the purpose of properly sealing the gears on the side faces thereof,1 have provided a special arrangement of coaxially adjustable endplates, bushings, or bearings, sometimes herein referred to as bushingbearings, with fluid pressure actuating means. The bearing is indicatedgenerally at in, and this bearing in the modification shown, togetherwith the means for controlling it, form the subject matter incombination to which the present invention is directed.

The gear journal for each gear has interposed between it and theenclosing housing a specially constructed axially adjustable bearingbushing, nut for journal ISA being indicated at 2i, and including aradially extending flange or piston portion 22, sealably fitting thebore receiving the gear it, but having an axial thickness less than thespace receiving the same to thus provide an annular high pressureactuating chamber 23 for the purpose to be described. Thus bearing 20further includes an axially extending tubular portion 24, received inreduced bore 25 and sealed with reference thereto by a flexible sealring 26.

In a particular part of my invention. a piston 21 is formed as anextension of tubular portion 24 of bushing assembly 2|. As will beapparent from other figures, the piston member 21 may be equally wellformed separately from bushing assembly 2i so long as the same isarranged to apply axial pressure to bushing assembly 21.

Piston member 21 is sealed with reference to the bore 28, in which thesame operates, by means of a flexible sealing ring 28. A passage 21Aleads from the interior of tubular extension 24 for the purpose ofplacing the same in communication with the low pressure side of the pumpas will appear. I contemplate, in the preferred embodiment 9. separatepiston (not shown) identical to the piston 21, for cooperation with thebushing assembly of gear l4. However, it will be apparent that a singlepiston 21 may be made to apply the necessary axial pressure to both ofthe bushings on one side of the gears.

Discharge fluid pressure is delivered to chamber 23, there applying afirst axial force Pl to bushing assembly 2|, by way of small checkvalves 3| or 32, depending upon the direction of rotation and hencewhether the flow passages i6 or H form the outlet passage, then throughpassages 33 and 34. Passage 33 also leads to the piston member 21 foroperating the same to thus supply an additional axial force P2 forurging bushing 2! into engagement with the side or face of gear l5. Itis important to note that the effective pressure area of the back sideof bushing flange or piston portion 22, in chamber 23, together with thepressure area of the piston 21, are made such that the total of coaxalforces Pi and P2, acting to press bushing flange 22 into contact withgear i5 is always slightly greater than the opposing coaxial force P3 ofthe fluid attempting to force the bushing bearing 22 away from the gear,this difl'erental. being only a small fraction of the outlet pressure.This is always true when the pump is operating as a pump, regardless ofhow h1gh-the output pressure may become. It has been observed that evenwhere the output pressure may be in the neighborhood of several thousandpounds per square inch. the diiference between the sum of PI plus P2 onthe one hand and P3 on the other is still only a small amount, a fewpounds for example. It will then be seen that so long as there extends asmall increment of pressure in the direction of bushing engagement withthe gear, the bushing can never be forced away from the gear by fluidpressure exerted between the gear and the bushing.

Referring to gear H, it will be apparent that an identical bushingconstruction will be provided including a piston member, the same notbeing shown since it is believed to be apparent from a disclosure anddescription of the structure associated with gear [5.

It will be important to note that the small differential pressuretending to maintain engagement is always present during the pumpingaction, irrespective of whether the pump is operating at a relativelylow pressure or a very high pressure. In other words, the pressure ofthe frictional engagement between the bushing and the associated face ofthe gear does not vary appreciably with a change in output pressure fromlow pressure to a pressure substantially equal to the maximum of thepump, but this pressure differential urging the bushing into contactwith the gear always preferably remains at a very low value, as it isusually only necessary, as above pointed out, that the same be a smalldiflerential greater than the pressure between the bushing and the gear,tending to separate the same.

For the purpose of releasing excess fluid pressure in the assembly onthe low pressure side of the bushing 2i, passage 35 leads alternativelyto check valves 36 or 31, depending again upon whether passage lb or IIis the high pressure side.

Gears i4 and I! are preferably provided on the opposite side thereofabout the associated Journal, with similar bushing bearing assemblies,but not necessarily having axial adjustment. Bushing bearing II for gearI5 is shown in Fig. 1 with a tubular extension 4|, said extension havinga flexible seal Ha interposed between its outer periphery and thehousing II. The corresponding bushing for gear I is not shown, for thepurposes of simplicity. In addition, the well known elements of thepresent type of pump are contemplated, but a detailed description andshowing thereof are unnecessary to an understanding of the presentembodiment and have been omitted for the purposes of clarity.

Referring next to the construction shown particularly in Fig. 3, thereis provided a modification wherein there is preferably a combinedmetering and release valve, shown in its entirety at 50, interposedbetween the pressure loaded bushing and the outlet pressure side of thepump, that is, the high pressure side of the pump. In other words, thereis a metering valve and a release valve in the circuit comprising thefluid connection to the main flow passages. In the arrangement shown inFig. 3, this metering and release valve is manually adjustable wherebythe pressure necessary to effect a release upon a maximum desired loadmay be varied if desired.

As shown in Fig. 3, there is provided a bore in the pump housing, hereindicated as the axially extending bore 52. This bore 52 is preferablyprovided with a reduced portion forming a port 54, leading into the highpressure chamber between the end of the bearing member 20, and the pumphousing. This high pressure chamber may be designated as the highpressure chamber 58, for purposes of reference.

Seated on an annular ledge portion 58 formed by the reduced bore for theport 54, is a valve 80, the stem of which is here shown as extendingaxially of the bore 52, and which stem has a guide portion or spider 82.This guide portion 62 is provided with cutaway portions whereby fluidmay flow past it, but the said portion 62 "rides in" the bore 52, toassist in maintaining the valve stem in axial alignment with the bore.

The bore 52 is likewise provided with an insert M, which is spaced fromthe port 5| to form a low pressure chamber 66, and which insert 64 has ahole or passage through the center thereof in which the valve stem ofthe valve 60 moves. This valve stem for the valve ill preferably has aclose sliding flt in the insert, one which is substantially liquidtight.

Spaced axially from the insert 64, toward the outer end of the bore ii!is a collar 68. The stem of the valve Gil passes through this collar 68,and there is sufllcient clearance between the stem and the collar toefl'ect a metering action of fluid passing therebetween. A space betweenthe collar 68 and the insert 64 comprises a high pressure bore chamberIII, which communicates with the outer end chamber 12 of the bore 52 bymeans of the metering passage around the valve stem ill through thecollar 88.

The outer end of the bore 52 is closed by a plug H which is externallythreaded to engage internal threads in the bore 52 and which is ad-Justable by threading into and out of bore I2 for the purposehereinafter set forth.

The plug II engages a spring I8 which seats on the portion 82 of valve80, the pressure on the spring 18 exerted by the plug I4 determining thepressure in the high pressure chamber 56 necessary to unseat valve 6|)from the shoulder portion 58 and relieve excess pressure in the highpressure chamber 56.

The high pressure bore chamber 10 is placed in communication with theannular high pressure chamber 23 and with the high pressure chamber 56by means of one or more passages 18 for fluid. This is obvious from anexamination of Fig. 3. The low pressure chamber 66 is placed incommunication with the low pressure side of the pump by means of one ormore passages 8|) discharging into the main flow passages IE or I! asthe case may be. Valve means, here shown as the spring pressed ballvalve 82, closes the low pressure passage to the inlet of fluid from thehigh pressure side of the pump but permits fluid under pressure in thelow pressure passage 80 to escape into the low pressure side of thepump, that is into the "inlet" conduit formed by the main flow passageIE or II as the case may be, depending upon the direction of rotation ofthe pump. It is believed this operation is obvious from the figure.

The chamber 12 is placed in fluid communication with the high pressureor outlet side of the pump being the main flow passage IE or i'l,depending upon the direction of rotation of the gears. This isaccomplished by means of passages 86. These passages are provided withvalves 88 which operate in reverse to the valve means 82. These valves88 are operable on the high pressure side of the pump, the pressurebeing taken from the main flow passages Iii or H, depending upon thedirection of rotation of the pump. Their operation is believed obvious.

The operation of the pump shown in Fig. 3 is as follows. Assume that thegears are rotating in a direction so that the high pressure side of thepump is the main flow passage l1, and that the low pressure side is themain flow passage iii, the fluid flowing to the pump in the passage l6will be placed under pressure and will enter passage II from where itwill be conducted to the device operated by the fluld pressure. Thepassage ll however will discharge a small quantity of its fluid into thepassage 86 past the valve ill! from where it flows into the chamber 12.Upon entering the chamber 12 it will pass the portion 62 of the valveGil, and be metered between the stem of the valve so and the collar 68.This metering action will cause the fluid pressure in the high pressurechamber 10 to rise and will conduct such fluid pressure through thepassages 18 into the high pressure chamber 55 at the end of the pistonand into the annular high pressure chamber 23 about the annular flangeportion of the bearing or piston.

Since the bushing area subject to pressure in the chamber 56 and theannular chamber 23 is greater than the loaded area on the gear face sideof the bushing, the amount of pressure will be suihcient to maintain thebushing bearing in engagement with side face of gear ii. In thisconnection, a low pressure area on the portion of the hearing which maybe called the underside or gear side, at the end, is created by the portmeans OI which discharges into the hollow end portion of the shaftforming the trunnion for the gear II, from where it may be carried tothe low pressure area or discharged outside the pump as desired. Thisrelieves pressure due to leakage between the pump and the side of thebearing. These port means may terminate in an annular portion asindicated in Fig. 3 whereby all entrapped fluid will be relieved throughpassage 80, as shown by the dotted lines.

When the pressure in the chamber 56 and in the annular chamber 23reaches a predetermined regulable amount, it will raise the valve Bilfrom its seat on the ledge portion I58 and allow any excess pressure toescape into the low pressure chamber 68 from which it is conducted intothe low pressure side of the pump through passage Oil. The pressurenecessary to relieve this valve may be adjusted by manual manipulationsof the plug 14 by threading it in or out. If desired a longer stem thanthat shown to the valve Bil may be provided, so that it will touch theplug I4 when the plug is threaded into the bore a maximum distance, forthe purpose of locking the release valve against operation. With thisarrangement, of course, any pressure in the outlet of the pump would bereflected to the movable bushing bearing through the metering means,regardless of the amount of the pressure.

Due to the operation of the valves 88 and 82, as is obvious from thedrawing, the pump may be run in either direction and identical loadingaction will take place.

Referring next to Fig. 4, there is here shown schematically the pressurediagram for the gear pump, by which location of the centers of pressuresloading the movable bushings, especially in Figs. 5, 6, '7, 8, 9 and 10,hereinafter referred to, may be determined. This schematic arrangementof Fig. 4 is self-explanatory, but it may be noted that the location ofthe pistons as indicated in Figs. through 10 should be such that theyare approximately centered on the points Pl and P5, for each gear wheel.

For the rotation of the gears in one direction, the point P5 representszero points per square inch, while the point P4 represents approximatelymaximum points per square inch. It is understood upon reversal ofdirection of rotation, the point P5 would be the high pressure point andPI the low pressure point. Each of the gears of the gear pump has acorresponding pressure diagram substantially as that shown in Fig. 4.

As shown in this schematic drawing, the maximum pressure is assumed tobe 1,000 pounds per square inch. Referring next to Figs. 5, 6, and 'i,there is shown a modified form of construction in which the bushingbearing is pressure loaded by means of separate pistons, preferably solocated that the pressure exerted by the pistons on each portion of theperiphery of the bearing is in proportion to the outward pressureexerted on the corresponding bearing space adjacent the pump gear, andin which the separate pistons may be loaded in different amountsdepending upon the direction of the rotation of the gear wheels, amongother things.

For simplification in manufacture, and to secure a more direct thrust onthe bearing for pressure loading of the bearing, the bushing bearingHill, which is a movable bushing bearing in connection with gear wheelII, and the bushing bearing it! which is the corresponding movablebushing bearing in connection with gear wheel I. have been shown ashaving the flange portion shown in Figs. 1, 2, and 3 eliminated.Likewise. the bushing bearings IM and "i8, which are the fixed bushingbearings, are devoid of flange portions. Flange portions may be added,if desired. The movable bushing hearings in and in are movable axiallyon the gear wheel trunnion in the same manner that the bushing bearingIi was movable in connection with the trunnion Ila. There is preferablya low pressure area at the end of each trunnion for the gear II and I!on the movable bushing side, said low pressure chamber for the movablebushing end being numbered I08 and forming a chamber space into whichthe movable bushings may be moved. Located in reduced axial extensionsH0 0! the bore forming the chamber lliB, are the separate pistons H2 andIII which bear against the edges of the bushing bearings I00 and I02, onone side thereof as is clear from the drawings. Preferably these pistonsare so located that they are adapted to exert pressure against the edgeportion directly in axial line with the edge portion receiving the mostoutward pressure from the fluid in the gear II. lit is understood,however, that the pistons may be located in any convenient position andthat more than two for each "side" of the pump may be provided. SpringsIII are provided for exerting a relatively light pressure on each of thepistons urging the respective bushing in the direction of the gear wheelby an amount sufficient to overcome inertia and friction.

As is apparent from the drawings, Figs. 5, 8, and 7, the pistons on eachside of the pump are loaded separately. Thus the pistons III and Ill areloaded and controlled by means of fluid entering through a meteringvalve H8, while the pistons H3 and H5 are loaded in control by theadjustable metering valve I20. To economize on space and provide a morecompact construction, the bores for metering valves H8 and III! areshown as extending across the pump housing instead of axially as inFig. 1. Either arrangement is equally operable, however, and the choiceis one of manufacturing and design advantage.

It will be apparent from the figures, that metering valve I is receivesits pressure, if any (depending upon the direction of rotation of thepump), from the main flow passage l1, while the metering valve I20receives its fluid from and is controlled by. the fluid in the main flowpassage ll. Except in their low pressure chambers, the structuresforming the metering valve and housing therefor are not connected. Thelow pressure chambers preferably are connected by passage 660, sincethey each will have to have an outlet to the low pressure side.

As is clear from examination of Figs. 5, 6, and 7, the construction ofthe metering valve and release valve in and I20 may be the same asprovided in connection with the assembly III of Fig. 3. However, I havedisclosed a slightly modifled construction generally similar to that ofFig. 3, except that instead of the plug 14, I have provided a modifiedclosure and adjustment means. This comprises a member I22 which isinternally and externally threaded to be inserted into one of the boresof the housing and which carries a threaded insert IN. The caps I28 maybe provided to thread down on the threaded insert and hold the latter inposition much in the nature of a lock washer or member, while providinga better seal than would be the case without the cap. The insert I isslotted for adjustment with a screw driver or may be otherwise providedwith adiusting means by which it may be moved up or down in the meteringvalve bore whereby the tension on the spring holding the valve seatedmay be regulated. Otherwise, the valve arrangement is generally similarin construction to that shown in Fig. 3.

The inlet from the high pressure conduit, which may be the passage I28or I30 as the case may be, depending upon the direction of rotation ofthe pump gear, communicates with the chamber I2 of the respective valvebores. In the low pressure chambers 00, the passage 80 leads from bothvalves and has intercommunication so that the discharge may be to thelow pressure side of the pump regardless of whether it is the main flowpassage I8 or the main flow passage I'I. Check valves 02 are generallysimilar to those of Fig. 3, except that the assembly is slightlydifierent in an inconsequential manner from a patentable standpoint.

The construction oi both metering valves in Fig. 5, Fig. 6, and Fig. 7may be identical and only one is described for purposes of clarity.

The operation or the device shown in Figs. 5, 6, and 7 follows and it isassumed, i'or the purpose of describing it, that the fluid'enters thepump through the low pressure main flow passage I and, after the pumpingoperation, is forced out through the high pressure main flow passage II.In order to load properly the bushing I00, the pistons H2 and H4 willhave to be loaded, while it is unnecessary ordinarily when the directionof rotation is as indicated, to load the pistons I II and H0. Fluid fromthe passages II will enter the passages I28 and flow to the valve H8 inthe same manner as it flowed to the valve 50.

There the fluid will be metered and conducted through the passages I32to load the pistons II2 and H4 which load the bushings. When thepressure reaches a certain predetermined amount, the excess fluid willpass through the discharge port 54 and will raise the valve II8 from itsseat, allowing excess pressure to escape through the low pressurepassage 00 into the main flow passage II. In such arrangement, there isno need for a valve in the passage I20 similar to the valve 08 sincethere is no inter-communication between the chambers I2 for the twometering valves.

Upon reversal oi the pump the other metering valve I20 will operate,while the valve IIB will remain unloaded. The pressure, upon reversalpump, in the main flow pipe I! will be low, and will allow the valve II8 to unseat and the pistons H2 and I I4 to move out oi pressure loadedposition. In such latter event, the pistons II: and II! will beseparately operated and will have no communication 01' fluid pressurewith the pistons II! and H4.

Refer next to the modifications shown in Figs. 8, 9, and 10. There isprovided a more simple and compact means of piston loading the bushingbearing I00 and its companion bearing I02, by means of two sets ofpistons operated without the metering valve but having a release valvefor each pair of pistons.

As shown in the drawings, the pump and bushing arrangement may be thesame as that of Figs. 5, 6, and '7, except that the metering valve III!and the metering valve I20 have been removed from the assembly. As shownin these figures. the pistons II2, III, Ill, and II! are arranged inapproximately the same way as are the similarly numbered pistons ofFigs. 8, 9, and 10. The high pressure main flow passage II, for example,

is connected to the chamber I24 for the pistons on one side of the pump,that is, for pistons I I2 and H4 by means or passages I36 and I38respectively. With this arrangement, when the main flow passage I0 isthe low pressure area and the inlet side of the pump, the pistons H3 andIII are entirely unloaded, and the pistons H2 and H4 are fully loaded.Upon reversal of the pump, the pistons H3 and II! will be loaded whilethe pistons H2 and H4 will be allowed to unload through their passagesI20 and I38 into the main flow passage II. In this arrangement there isprovided a low pressure area at the end of the bushing I00 and I02. Thisarea, herein referred to as space or chamber I40, in reality could bemore properly termed an intermediate pressure area in that the pressuresare fluid pressures of relatively low amount, escaping along the shaftof the gear and around the piston by leakage, and which enter the spaceI40 and are conducted by the passage I42 into the discharge area I44.This pressure displaces the ball valve I40 or I40, depending upon whichone is on the low pressure side, and escapes through the piston chamberinto the inlet side 01' the pump. The passage I50 for each side or roupof pistons acts as the conduit for the escape oi this relatively minutequantity of fluid. It is noted that the spring loading on one of theballs I46 or I40, must be displaced by this minute quantity of fluid,and the pressure necessary to do this furnishes sufficient fluid aroundthe trunnions and hearings to lubricate them.

The passages I52 and I54 correspond in function to the passages I36 andI38 except that passage IH leads from the piston II3 to the main flowpassage l5 and the passage I54 leads from the piston I I5 likewise tothe main flow passage I6.

It may be understood that with the arrangement shown in Figs. 8, 9, and10, the end plate of the housing is materially reduced in size and ismore compact and lighter. This is an important feature where such pumpsare used in the limited space provided in airplanes, for example, andwhere it is desired to cut down the weight of the pump.

Numerous details or the various figures are obvious and apparently donot need specific description. For example, in Fig. 8 the shafts ortrunnions for the gear wheels are both shown as hollow, so that seepagefluid at the ends of the trunnions may be conducted back therethrough tothe space I40 where it escapes in the regular way.

While I have described my invention in connection with one specificembodiment thereof, it is to be understood that this is by way ofillustration and not by way of limitation, and the scope of my inventionis defined solely by the appended claims which should be construed asbroadly as the prior art will permit.

I claim:

1. In a. gear type high pressure liquid displacement dlevice includingmeans defining a housing having a .pair of parallel overlappingcylindrical bores, gears in said bores having teeth meshing in the areaof said overlapping, said gears having pairs 01' oppositely extendingjournals, a plurality oi bearing insert bushings received in said boresabout said journals and in engagement with the side faces of said gears,means responsive to the outlet pressure on either side of said gearsdependent upon the direction of rotation thereof, eiIective toselectively communicate said outlet pressure to the said bushings on atleast one side of said gears urging the bushings into sealed relationtherewith, including means comprising separate pistons bearing againstthe ends of said bushings and communicating through pressure meteringmeans with the outlet pressure from said gear pump. and valve means inconnection with said pressure metering means relieving the fluidpressure on said pistons above a desired predetermined amount.

2. In a device of the class described a gear pump, movable bushing meansadjacent at least one face of each 01' the gears 01 said gear pump,piston means bearing on said movable bushing means. means loading saidpiston means from the outlet pressures existing in said gear pump, saidlast mentioned means including pressure metering means and adjustablevalve means actuated by excessive pressure over a predetermined amounton said piston means for relieving the excess pressures on said pistons.

3. In a device of the class described. a Bear pump, including movablebushing means adjacent one face of each of the gears oi said gear pump,piston means bearing on said movable bushing means, means loading saidpiston means irom the outlet pressures existing in said gear pump, saidlast mentioned means including pressure metering means and adjustablevalve means actuated by pressure exceeding a predetermined amount onsaid piston means for relieving the excess pressure on said pistonmeans. and said piston means being so positioned that the resultant ofthe forces impressed thereon opposes the resultant of forces acting inan opposite direction on the bushing means.

JOHN A. LAUCK.

REFERENCES CITED The following references are of record in theCertificate of Correction Patent No. 2,444,165.

June 29, 1948.

JOHN A. LAUCK It is hereby certified that error appears in the printedas follows: Column 11, line 20, claim 2, for the that the said LettersPatent should be read with numbered patent requiring correction wordpistons read piston means; and

specification of the above this correction therein that the same mayconform to the record of the case in the Patent Oflice.

Signed and sealed this 28th day of September, A. D. 1948.

THOMAS F. MURPHY,

Assistant osmium of Patents.

ings on at least one side of said gears urging the bushings into sealedrelation therewith, including means comprising separate pistons bearingagainst the ends of said bushings and communicating through pressuremetering means with the outlet pressure from said gear pump. and valvemeans in connection with said pressure metering means relieving thefluid pressure on said pistons above a desired predetermined amount.

2. In a device of the class described a gear pump, movable bushing meansadjacent at least one face of each 01' the gears 01 said gear pump,piston means bearing on said movable bushing means. means loading saidpiston means from the outlet pressures existing in said gear pump, saidlast mentioned means including pressure metering means and adjustablevalve means actuated by excessive pressure over a predetermined amounton said piston means for relieving the excess pressures on said pistons.

3. In a device of the class described. a Bear pump, including movablebushing means adjacent one face of each of the gears oi said gear pump,piston means bearing on said movable bushing means, means loading saidpiston means irom the outlet pressures existing in said gear pump, saidlast mentioned means including pressure metering means and adjustablevalve means JOHN A. LAUCK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 944,708 Vollmann Dec. 28, 1909 201,475,693 Carrey Nov. 27, 1923 1,673,261 Meston et a1 June 12, 19282,044,873 Beust June 23, 1936 2,159,748 Miller et a]. May 23, 1939 22,212,994 Vrolix Aug. 2'7, 1940 Certificate of Correction Patent No.2,444,165.

June 29, 1948.

JOHN A. LAUCK It is hereby certified that error appears in the printedas follows: Column 11, line 20, claim 2, for the that the said LettersPatent should be read with numbered patent requiring correction wordpistons read piston means; and

specification of the above this correction therein that the same mayconform to the record of the case in the Patent Oflice.

Signed and sealed this 28th day of September, A. D. 1948.

THOMAS F. MURPHY,

Assistant osmium of Patents.

